2- ".............. the human being is the most argumentative creature." 18:54
3- "Due to their transgressions, We prohibited for the Jews good foods that used to be lawful for them ......" 4:160
From verse 1 we learn how God made the religion easy for us to follow and that God does not want for us any hardship in practicing the religion.
From verse 2 we read how God describes the human being as the most argumentative creature. We know that all too well and we also know how the human being has a tendency to complicate what God made simple and easy to follow.
From verse 3 we read how God prohibited certain items on the people of Israel simply because they have prohibited these items on themselves.
Now when we read 2:67-73 we start to grasp the message of all these verses together.
God commanded the people of Israel to perform a simple and un-complicated act, that being to slaughter a Heifer. However, those who received this command were not happy performing it in its simple form. They kept asking God for details that were not required in the initial command. As a result of their argumentative nature and their attempt to complicate God's commands, God placed additional requirements that will make it harder on them. Initially, the command was simple and easy to follow, but due to their argumentative nature God made it more difficult on them.
Some would have simply got any heifer and slaughtered it, they would have been in complete harmony and obedience to God's simple command, but others will say "the command does not include all the details ... etc", and as a result of not being satisfied with God's simple commands, they incur more burden on themselves.